The invention relates to surgical methods and apparatus, and in particular the invention is directed to improved methods and apparatus for precision laser surgery. In one preferred embodiment, the system of the invention is used for effecting precise laser eye surgery. In other embodiments the invention is applicable to non-surgical diagnostic procedures or non-medical procedures involving precision laser operations, such as industrial processes.
Beginning in approximately 1960, largely due to the work of Dr. Littman at Carl Zeiss, the first surgical microscopes were introduced. Prior to that time, surgeons who required a more magnified image of the region in which they sought to operate used a special set of loupes that have magnifying lenses attached to the lower portion of the spectacles, especially in ophthalmology but also in otoringology and other specialties. In other disciplines such as urology and internal surgery, barrel type endoscopes were used.
Due in part to the pioneering work of Dr. Joaquin Barraquer, the surgical microscope came into wide use in ophthalmology; at first for corneal transplant surgery and later for cataract surgery among other procedures. The levels of magnification, zooming capabilities, and definition of the work region provided the surgeon the means to better direct his surgical invasions. The end result was increasingly more accurate surgical procedures with less trauma to the patients and a lowered level of complications arising from surgery.
The early successes with now conventional surgical microscopes based on direct optics for observing a target image, gave rise to the creation of several ophthalmic study groups, most notably the International Ophthalmic Microsurgical Study Group ("IOMSG"), to promote new concepts and techniques in microsurgery. Since their inception in 1966, the invited reports presented at the IOMSG meetings have been published by Karger, Basel as their Developments in Ophthalmology series.
The advent of microsurgery brought on by the use of surgical microscopes rekindled interest in the ophthalmic community for the pioneering of increasingly more accurate surgical procedures. In their continued quest for accuracy and control, ophthalmologists eventually turned to another of the discoveries which occurred around 1960, the laser.
During the 60s, 70s, and 80s, lasers were used extensively in ophthalmology and have now become a commonplace tool in most surgical specialties' instrumentalia. There are several distinct advantages to the laser as a scalpel replacement which have come into evidence.
Since a laser's energy is composed of light photons, by selecting the wavelength of the laser emission to correspond to the preferential absorption band of an imbedded tissue, a laser can be deemed to perform "non-invasive" surgery, in that the surgeon need not perforate the overlying tissue layers in order to generate an effect at a prescribed depth.
Biological tissues are, however, broad band absorbers of energy, albeit not uniformly so. In practice therefore, "non-invasive" laser surgery corresponds to the effort to minimize the laser energy deposition onto the living tissues on the way to and directly behind the targeted tissues along the optical path of the laser beam when compared to the energy deposition at the intended target.
During the early 1980s, Dr. Aron-Rosa (U.S. Pat. No. 4,309,998) introduced a mode locked Nd:YAG laser for use in Ophthalmology which claimed to evidence plasma decay induced generation of outwardly expanding shock waves. Dr. Frankhauser (U.S. Pat. No. 4,391,275) claimed a somewhat similar result using a Q-switched Nd:YAG laser. Ultrashort pulsed lasers have now established themselves as the modality of choice for many surgical procedures where propagating thermal effects are to be suppressed.
In 1986, this approach was taken one step further by development of an excimer pumped dye laser (not to be confused with an excimer laser which, due to the highly energetic photons characteristic of ultraviolet lasers, are characteristically penetrative photoablative lasers--See Trockel, U.S. Patent Pending, Schneider and Keates, U.S. Pat. No. 4,648,400, Srinivasian, U.S. Pat. No. 4,784,135, and L'Esperance, U.S. Pat. No. 4,665,913) which could predictably cause plasma effects with significantly less pulse energy than previously demonstrated. (See Ferrer and Sklar, Vol. XIV, Developments in Ophthalmology, Karger 1987, and Troutman et al. in the same Volume and in Trans. of Am. Ophth. Soc. 1986).
Laboratory experiments conducted by the applicants herein (unpublished) showed that imbedded cavities of diameters smaller than 0.5 micrometers are possible provided that tightly contained plasmas could be generated with a less than 0.5 millijoule pulse. The importance of the smallness of the induced lesions is related to the accuracy and error tolerances which can be achieved by the guidance and delivery systems of surgical instruments using such lasers. Lasers today are varied. It is well appreciated that the limitations on the achievable accuracy and control of laser surgical instruments today is no longer paced by the development of laser technology, but by the imaging and tracking technologies needed to effectively use the laser.
An understanding of current practices and the range of instruments in use for target acquisition, target recognition, and target tracking is helpful in order to appreciate the limitations of the current technologies. The principal instruments used today, for example in ophthalmology, for targeting diagnostics and inspection are (1) the surgical microscope, (2) the slit lamp microscope, (3) the keratometer, (4) the pachymeter, (5) the corneoscope, (6) the specular microscope, (7) the A&B ultrasonic scanners, and (8) the fundus camera. (There is a host of additional equipment used to determine intra ocular pressure, tonometers, tensiometers, perimeters for visual field testing, and the various devices used to approximate the eye's refraction.) Items 1, 2, and 8 provide the surgeon with an image of his target. Items 3, 4, 5, 6, and 7 provide the surgeon with measurements of specific dimensions of a patient's eye and condition.
These instruments have proven efficacious to within previously acceptable tolerances.
It is an object of the present invention to accommodate much more demanding tolerances in laser surgery, particularly eye surgery but also for other medical specialties, through a method, apparatus and system for high-precision laser surgery which provides the surgeon "live" images essentially in real time, containing the full supporting diagnostic information about depth and position at which a surgical laser will be fired. In a computer, the full information content of a given signal is interpreted so as to provide this supporting diagnostic information, and the resulting accuracy achievable is within a few human cells or better. It is further within the scope of this invention to provide non-surgical tools for measurement of the entire refraction of the eye rather than relying solely on the approximate curvature (keratometric "k" readings) of the anterior surface of the cornea. This calls for curvature readings of all of the reflective surfaces of the eye and allows for measurement of astigmatism and accommodation between the various optical components of the eye.